Recently, the power system equipped in elevator contains motor and gear reducer to get large output torque. In general, the motor and gear reducer are designed and manufactured separately. Its chief advantage is the reducing complexity of the related design process. However, the power system would constitute a variety of problems such as larger amount of components, heavy weight, longer power-path, and large installation space. The purpose of this paper is to present new design concept which integrates motor and gear reducer into one single device and named as "gear-motor". This concept has advantages: 1. less friction loss and higher overall efficiency, 2. smaller volume, less weight, and less axial space, and 3. better dynamic characteristic, less vibration, and less noise. First, according to the combining and eliminating methods of check list, we proposed four design concepts "gear-motor". Based on the concept of train value equation of the train circuit, the 2-stage planetary gear reducer and coupled type gear reducer are synthesized. Then, according to the latent power theorem, the meshing efficiencies of the corresponding gear reducers are analyzed to be 95.46% and 95.87%. Finally, the engineering design is accomplished to illustrate the design methodology. Based on the proposed methodology, all gear-motors can be synthesized.